Chapter 9 Study Guide: Solutions

Chapter 9: Solutions

Introduction to Solutions

Solutions are homogeneous mixtures composed of two or more substances. In chemistry, understanding solutions is essential for studying reactions, concentrations, and properties of mixtures. This chapter covers the definitions, properties, and calculations related to solutions.

• Solution: A homogeneous mixture of two or more substances.

• Solute: The substance that is dissolved in a solution (present in lesser amount).

• Solvent: The substance that dissolves the solute (present in greater amount).

• Electrolyte: A substance that conducts electricity when dissolved in water.

• Nonelectrolyte: A substance that does not conduct electricity when dissolved in water.

Key Terms and Concepts

• Solubility: The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.

• Saturated Solution: Contains the maximum amount of solute that can dissolve at a given temperature.

• Unsaturated Solution: Contains less solute than the maximum amount that can dissolve.

• Supersaturated Solution: Contains more solute than is normally possible at a given temperature (unstable).

• Miscible: Liquids that dissolve in each other in all proportions.

• Immiscible: Liquids that do not dissolve in each other.

• Precipitate: A solid that forms when two solutions are mixed and an insoluble product is produced.

Properties of Solutions

• Homogeneous Mixture: Uniform composition throughout.

• Solubility Rules: Guidelines used to predict whether an ionic compound will dissolve in water.

• Concentration: A measure of the amount of solute in a given amount of solvent or solution.

Concentration Units

Several units are used to express the concentration of solutions. The most common are molarity, mass/volume percent, and parts per million (ppm).

• Molarity (M): Moles of solute per liter of solution.

• Mass/Volume Percent (% m/v): Grams of solute per 100 mL of solution.

• Mass Percent (% m/m): Grams of solute per 100 g of solution.

• Volume Percent (% v/v): mL of solute per 100 mL of solution.

• Parts per million (ppm): mg of solute per kg of solution (or per L of water for dilute aqueous solutions).

Key Equations

• Molarity: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Dilution Equation: $C_1 V_1 = C_2 V_2$ Where $C_1$ and $V_1$ are the initial concentration and volume, $C_2$ and $V_2$ are the final concentration and volume.

• Mass/Volume Percent: $\% (m/v) = \frac{\text{grams of solute}}{\text{milliliters of solution}} \times 100$

• Mass Percent: $\% (m/m) = \frac{\text{grams of solute}}{\text{grams of solution}} \times 100$

• Volume Percent: $\% (v/v) = \frac{\text{milliliters of solute}}{\text{milliliters of solution}} \times 100$

Electrolytes and Nonelectrolytes

Electrolytes are substances that dissociate into ions when dissolved in water, allowing the solution to conduct electricity. Nonelectrolytes do not dissociate into ions and do not conduct electricity.

• Strong Electrolytes: Completely dissociate in water (e.g., NaCl, HCl).

• Weak Electrolytes: Partially dissociate in water (e.g., acetic acid).

• Nonelectrolytes: Do not dissociate (e.g., sugar, ethanol).

Solubility and Factors Affecting It

• "Like dissolves like": Polar solvents dissolve polar solutes; nonpolar solvents dissolve nonpolar solutes.

• Temperature: Solubility of solids generally increases with temperature; solubility of gases decreases with temperature.

• Pressure: Affects the solubility of gases (Henry's Law).

Sample Problems and Solutions

• Example 1: Dilution Calculation How many milliliters of 8.0 M HCl solution would you need to make 0.50 L of 2.0 M HCl? Solution: $C_1 V_1 = C_2 V_2$ $8.0\,M \times V_1 = 2.0\,M \times 0.50\,L$ $V_1 = \frac{2.0\,M \times 0.50\,L}{8.0\,M} = 0.125\,L = 125\,mL$

• Example 2: Mass/Volume Percent What is the % (m/v) of a solution made by dissolving 5.0 g NaCl in enough water to make 100 mL of solution? $\% (m/v) = \frac{5.0\,g}{100\,mL} \times 100 = 5\%$

Common Laboratory Techniques

• Preparing solutions of known concentration by dissolving a measured mass of solute in a specific volume of solvent.

• Using volumetric flasks and pipettes for accurate measurements.

• Performing dilutions using the dilution equation.

Summary Table: Types of Solutions and Examples

Type of Solution	Solute State	Solvent State	Example
Solid in liquid	Solid	Liquid	Salt water (NaCl in H2O)
Gas in liquid	Gas	Liquid	Carbonated water (CO2 in H2O)
Liquid in liquid	Liquid	Liquid	Alcohol in water
Gas in gas	Gas	Gas	Air (O2 in N2)

Additional info:

• Solubility rules are often provided on exams to help predict whether a precipitate will form in a reaction.

• Practice problems may involve calculating concentrations, preparing solutions, and predicting solubility.

• Understanding the properties of solutions is essential for laboratory work and real-world applications such as medicine, environmental science, and industry.